Processes for preparing polymers are well known in the art. However, many of the processes used to date to produce polymers for industrial use suffer from significant limitations, including high cost, significant gelation problems when a high degree of functionality is present, and an inability to produce polymers having particular desirable characteristics.
U.S. Pat. No. 4,414,370 discloses a continuous bulk polymerization process for polymerizing vinylic monomers to prepare low molecular weight polymers employing thermal initiation at reaction temperatures from 235.degree. C. to 310.degree. C. and residence times of at least 2 minutes in a continuous stirred reactor zone. The vinylic monomers of the disclosed process include styrenic monomers such as styrene and x-methylstyrene; acrylic monomers such as acrylic acid, methacrylic acid, acrylates, methacrylates; and other non-acrylic ethylenic monomers such as vinyl acetate.
U.S. Pat. No. 4,529,787 discloses a continuous bulk polymerization process including an initiator for preparing low molecular weight, uniform polymers from vinylic monomers at short residence times and moderate reaction temperatures to provide high yields of a product suitable for high solids applications. The disclosed vinyl monomers include styrenic monomers such as styrene and x-methylstyrene; acrylic monomers such as acrylic acid, methacrylic acid, acrylates, methacrylates, and functional acrylic monomers; and non-acrylic ethylenic monomers such as maleic anhydride and vinyl pyrrolidinone.
U.S. Pat. No. 4,546,160 discloses a continuous bulk polymerization process for polymerizing acrylic monomers to prepare low molecular weight, uniform, polymers for use in high solids applications which uses a minor amount of initiator at short residence times and moderate temperatures.
Various attempts have been made to improve the physical properties of polymers by replacing one type of polymerizable monomer for another, or by reacting a polymer with a group that will be incorporated into the polymeric structure. For example, U.S. Pat. No. 5,130,369 discloses a process for preparing functionalized polymeric compositions.
U.S. Pat. No. 5,521,267 discloses a process for preparing polymers from ethylenically unsaturated compounds containing acid groups with further ethylenically unsaturated compounds and monohydroxy compounds.
There has been no disclosure as to how a polymerization and condensation process can be performed in a continuous manner with high conversion such that gelation is avoided in such processes where cross-linking is possible due to multiple functionality on one or more of the components.
The polymer industry has long known that continuous polymerization processes are useful for obtaining large quantities of polymeric product. Furthermore, optimized continuous processes provide economic advantages over batch polymerization processes and may provide more uniform polymeric products. Additionally, many radically-polymerizable monomers containing desirable modifying groups are considerably more expensive than the precursors that they are made from. Thus, while continuous processes have been disclosed for the preparation of certain polymeric products for use in high solids coatings applications, a high temperature continuous process is needed for preparing polymeric products with improved characteristics achieved through reaction conditions and incorporation of a desired modifier in the reaction zone. Furthermore, a need remains for a continuous polymerization process in which a modifying agent may be incorporated into a polymeric chain with a high degree of conversion while also allowing for the architecture of the polymeric chain to be manipulated.